Is there a particular reason that you stop builds for OpenBSD and NetBSD? Those are fully compliant Posix systems and trying to compile OSS on these operating systems seems to me would help debugging the code. NetBSD in particular is in need of good audio support until 6.0 gets released but OpenBSD could also benefit from your drivers.

OSSv4 hasn't been ported (yet?) to OpenBSD or NetBSD, so no build is possible right now (There used to be an OSSv3.9 port, but I guess it's not reusable for OSSv4.1?). If someone will do the port (only the OS-layer needs to be written - most of OSS is portable), than I'm sure it will be accepted.